How to create a generic texture using python?
Name is no guaranty as another texture with the same name may exist. Use bpy.data.textures.new() and just pass a name as well as the modifier type: 

import bpy

# Get the object and context
C = bpy.context
ob = C.object

# Generate the texture and set the attributes
voronoi_tex = bpy.data.textures.new("displace_voronoi", 'VORONOI')
voronoi_tex.noise_intensity = .5
voronoi_tex.noise_scale = .5
voronoi_tex.nabla = .05

# Displacement modifier
disp_mod = None
for modifier in ob.modifiers:
    if modifier.type == 'DISPLACE':
        disp_mod = modifier        

if not disp_mod:
    disp_mod = ob.modifiers.new(name='MyVoronoiDisplace', type='DISPLACE')

# Assign the texture
disp_mod.texture = voronoi_tex
disp_mod.strength = .5
disp_mod.vertex_group = "Group"